This project has two long range objectives. It seeks an understanding of the photo-physical processes leading to lethal or mutagenic damages induced in DNA by UV-light; secondly, it undertakes to apply spectroscopic methods in obtaining structural information such as the conformation of RNA biopolymers. Specifically, we study the behavior of the triplet purin and pyrimidine base molecules: their phosphorescence decay characteristics, their zero-field EPR spectroscopy, their intersystem crossing pathways. We are particularly interested in the role played by C equals O and C equals S groups in the base molecules, their mechanism in enhancing spin-orbit coupling, and the extent hydrogen bondings rendered these mechanisms inoperative.